Tv turns on then shuts off in seconds

it sounds like the power switch has gone out it you might be able to remove the actual button itself and try pushing the switch with a rubber handled screwdriver

bad power supply u may have a bad capacitor on the power supply

so what should i do

Replace the deflection board. You can get replacement deflection boards from www.tvrepairworld.com

most likley the deflection board is at issue. Thats the number one board which fails in that chassis.

Trying installing a new power supply. This is the main problem with tv's with the issue. But if you just bought it I would try to get my money back from where I bought it from. Installing a power supply for a tv is not that hard at all.

Got the same problem following a message "Printer ink failure" code 0xc19a0035. Instructions say to shut down using button on/off. But printer refused to shutdown. After 30 minutes, I disconnected power cable. Removed cartridges. Reloaded cartridges. Reconnected power cable and got "Improper shutdown" message with continuous cycle. Solution: 1. While the printer is still turned on, unplug all cables and cords at the back of the printer.
2. Unplug the power cord also from the wall outlet...
3. Wait for two minutes.
4. Reconnect power cord to the wall outlet first.
5. Press and hold the pound (#) and six (6) buttons.
6. While holding down the two buttons, reconnect the power cord to the back of the printer and after two seconds, release pound and six buttons.
7. Turn on the printer if it turns off... and it's fixed.

Try a power drain and monitor if the TV continues to do this or not:
1. Unplug the product's power cable so the device is not grounded to the house. 2. Press and HOLD the product's own power button for 1 minute to drain the capacitors. 3. Plug the product back into a wall outlet and try to turn it on.
Note: This procedure works with battery operated devices as well so remove the batteries and hold down it's power button.  Electricity can remain in capacitors and on circuit boards enough to prevent normal functionality. By clearing the residue electricity, your product will have a fresh start and many times this will resolve a buggy or non-responsive device that appears to be dead.
If this doesn't resolve the issue, it's possible the power supply is on it's last legs.

does the power light blink? If so how many blinks does it blink